The present invention concerns a detection device which detects the leakage of oil.
Conventional detection devices for detecting the leakage of oil have been designed as follows: a detection sensor which is covered by a continuously porous polytetrafluoroethylene resin, which may be impregnated with powdered carbon, a conductive substance, so that two oil leakage sensing conductors such as copper wires are maintained at a fixed distance from each other is installed in a location where oil leakage is to be detected. When leaking oil penetrates this detection sensor so that the leaking oil is present between the two aforementioned oil leakage sensing conductors, the electrical resistance between the conductors increases, which resistance change can be measured, indicated that the oil leakage has occurred.
However, in the case of conventional oil leakage detection devices of the abovementioned type, the resistance-temperature coefficient of the continuously porous polytetrafluoroethylene resin impregnated with powdered carbon, which is used in the detection part, changes with a change in temperature. As a result, the electrical resistance between the oil leakage sensing conductors covered by this continuously porous polytetrafluoroethylene resin also changes with a change in temperature. Furthermore, the manner of this change is not always the same. For example, there are resins in which the resistance-temperature coefficient rises with a rise in temperature (as indicated by the dashed line in FIG. 2), and resins in which the resistance-temperature coefficient drops with a rise in temperature (as indicated by the dashed-dotted line FIG. 2).
Accordingly, in cases where such a detection sensor is installed in a location such as a drainage channel, where there are fluctuations in the water level, the degree of immersion of the detection sensor in the water varies with the fluctuation of the water level, so that there are abrupt variations in the temperature of the detection sensor. As a result, the electrical resistance between the two oil leakage sensing conductors changes as a result of the change in temperature even in the absence of any leakage of oil. Accordingly, the leakage of oil often cannot be accurately ascertained. Heretofore, this has been a problem in such conventional devices.
The present invention was designed in the light of such problems encountered in the prior art. The object of the present invention is to provide an oil leakage detection device whose detection characteristics are substantially unaffected by changes in temperature.